2005 Fiscal Year Final Research Report Summary
Research on resistivity structure of the source region of deep low frequency earthquakes in the crust
| Project/Area Number |
15540400
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Solid earth and planetary physics
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| Research Institution | Tohoku University |
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Principal Investigator |
MISHINA Masaaki Tohoku Univ., Graduate School of Science, associate professor, 大学院・理学研究科, 助教授 (70004421)
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| Project Period (FY) |
2003 – 2005
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| Keywords | volcanic front / resistivity structure / wide band MT sounding / deep low frequency earthquakes in the crust / water content of rock |
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| Research Abstract |
By the research in seismic velocity, for example tomography, it is known that the source region of low frequency earthquakes is near the low velocity area of the middle or the lower crust near the volcanic front in Northeastern Japan. It suggests that fluids in the crust are concerned to occurrence of low frequency earthquakes. The knowledge of the resistivity is very useful to investigate the role of the fluids to occurrence of the earthquake. In this research, wide band MT surveys were performed along three survey lines which pass through the epicentral areas of deep low frequency earthquakes near Mt.Yakeishi-dake, Mt.Kurikoma and Naruko volcano. The results are summarized as follows :
1.There exist remarkable low resitivity area in the middle and the lower crust to the west of the volcanic front in each three survey line.
2.Source area of deep low frequency earthquakes are near the rim of low resistivity area of the middle or the lower crust.
3.Resistivity of the low resistivity area in the middle or the lower crust is less than 10 Ohm-m. That means the majority of fluids consists of brine.
4.Almost all of microearthquakes in the upper crust occur in resistive areas.
5.Source regions of big earthquakes of 1962 Northern Miyagi and 1970 Southeastern Akita are connected to low resistivity areas of the middle crust. It suggests that fluid injected into the fault zone relates strongly the occurrence of big earthquakes.
6.Areas of low resitivity area in the middle and the lower crust, coincide areas of high strain rate revealed by GPS surveys.
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